muslin flats

I am currently designing a set for "The Drowsy Chaperone." Using fabric flats, and LED Pars from behind i would like to create the effect of having painted walls turn in to colored windows. My Idea is to custom build soft flats using medium wight Muslin, then on the backside make french window...

Okay I have built traditional muslin flats for a while and I normally use glue sizing (1 parts glue to 2 parts water) However, today I built some flats and applied the sizing and once dry found wrinkles everywhere. It seemed tight enough when I applied the sizing and it was covered. not sure...